Rubber products, such as tires, belts, hoses, etc., are reinforced with a reinforcing material such as steel cords, organic fibers, etc. In these rubber products, the rubber and the reinforcing material are desired to be bonded firmly to each other.
For bonding rubber and a reinforcing material, there is a method of using an adhesive. As one example, there is known a method of compounding and kneading an adhesive along with other various compounding ingredients in a kneading step of a rubber processing step, wherein a co-condensate obtained by further reacting resorcinol with a co-condensate obtained by reacting an alkylphenol such as p-tert-octylphenol, p-nonylphenol or the like with formalins is used as an adhesive in the rubber processing step (see PTL 1).
However, p-tert-octylphenol, p-nonylphenol are said to be candidate substances of SVHC defined in a regulation in EU states, REACH (Registration, Evaluation, Authorization and Restriction of Chemicals), and the possibility that use of the substances in EU states will be restricted is getting higher.
Given the situation, it is proposed to use alternative compounds not listed as candidate substances of SVHC defined in the regulation REACH so as to produce an adhesive to a reinforcing material. As one example, it is proposed to produce a co-condensate with resorcinol using p-tert-butylphenol in place of p-tert-octylphenol.
Further, it is preferable to reduce free components in the co-condensate in consideration of the working environment.